Apparatus for the production of hydrogen peroxide

ABSTRACT

The oxidation step in the anthraquinones process for producing hydrogen peroxide is carried out in a plurality of stages in an apparatus arranged for separating gas and liquid phases. The hydroquinone containing working solution is conducted in each stage in parallel flow from bottom to top with one oxygen containing gas. The stage with the highest hydroquinone concentration in the working solution is led to the gas mixture most depleted in oxygen and the fresh gas mixture is introduced into the stage which contains the working solution poorest in hydroquinone.

United States Patent 11 1 Liebert et al.

[ Apr. 29, 1975 [5 APPARATUS FOR THE PRODUCTION OF 2.902347 9/1959 Cosbyet al. 423/590 HYDROGEN PEROXIDE 2,966,398 12/1960 Jenney 260/369 X3,231,251 l/l966 r Scheibel 23/2705 T 1 Inventors: Martin Liebert,Frankfurt; Heinz 3.663574 5/1972 Yamagishi et al. 23/283 x Delle;Gerhard K'abisch, both of Rhemfelden of Germany PrimaryE.\'aminer.l0seph Scovronek [73] Assignee: Deutsche Gold-und AssistantExaminer-Barry l. Hollander Silber-Scheideanstalt vormals Attorney,Agent, or F irmCushman, Darby & Roessler, Frankfurt (Main), CushmanGermany Filed: Dec. 6., 1972 57 ABSTRACT [21] Appl' 312516 The oxidationstep in the anthraquinones process for Related U.S. Applicati Datproducing hydrogen peroxide is carried out in a plu- [62] Division ofsen 18356], Sept. 24, 1971, Pat' rality of stages in an apparatusarranged for separating NO- 3352335. gas and liquid phases. Thehydroquinone containing working solution is conducted in each stage inparallel 521 [1.8. CI. 23/283; 23/260; 261/21 flew from bottom to topwith one Oxygen Containing 51 1111. C1. B01f3/04; B01 j 1/00; COlb 15/022 The Stage with the highest hydrequinone concen- [58] Field 61 Search23/283, 260, 270.5 T; nation in the Working Solution is led to the gasrniX- 423 5gg 5 9 590; 2 21; 2 0 3 9 ture most depleted in oxygen andthe fresh gas mixture is introduced into the stage which contains the[56] References cu working solution poorest in hydroquinone.

UNITED STATES PATENTS 6 Claims, 3 Drawing Figures 2,180,888 11/1939Underwood 261/21 WJEK/Nf awn/rm 3/ f r-"2:17 I 3/4- Mail!- ..I L .2

APPARATUS FOR THE PRODUCTION OF HYDROGEN PEROXIDE This is a division ofapplication Ser. No. 183.561, filed Sept. 24. 1971, now Us. Pat. No.3.752.885.

The present invention is directed to an apparatus for the production ofhydrogen peroxide by the anthraquinone process and is especiallyconcerned with improving the oxidation step of this cyclic process.

It is known in this process to dissolve an anthraquinone derivative asthe reactor carrier in a solvent and to hydrogenate in the presence of acatalyst the working solution obtained so that about 50 percent of thequinones are converted into the corresponding hydroquinones. In theoxidation step, the hydroquinone solution is treated with an oxygencontaining gas whereby the quinone is reformed while simultaneouslyhydrogen peroxide is formed and then is isolated from the workingsolution. Most of the known process for isolating the H from the workingsolutions involve an extraction with water. By returning the workingsolution to the hydrogenation step and repeatedly rotating the individual steps there is obtained a cyclic process in which individualsteps there is obtained a cyclic process in which hydrogen peroxide issynthesized in practical manner from the gases hydrogen and oxygen (fromthe air) with the reaction carrier dissolved in the working solution.

In carrying out the oxidation industrially, there is the problemchemically to carry out the synthesis as quantitatively as possiblewhile avoiding breakdown reactions of the compounds of the workingsolution. In regard to carrying out the oxidation step industrially oneis concerned with carrying out the reaction in an energy saving mannerusing the smallest possible apparatus.

The chemical requirements are considered in a series of processes whoseimprovements consist, for example, in the production of extensivelyoxidation stable working solutions for example according to GermanOffenlegungsschrift 1,945,750 (Kabisch U.S. Application Ser. No. 69,151filed Sept. 2, 1970) or in the mode of action of regenerating breakdownproducts formed by the oxidation for example according to German Pat.No. 1,273,499. However, the oxidation step in the large industrialplants for the anthraquinone process today also not only requires moreenergy than the rest of the apparatus put together, but it also requiresproportionally by far the largest apparatus in the cycle. Thereforethere has not been a lack of proposals for industrially improving theoxidation step.

Thus in the former BASF plant the oxidation of the hydrogenated workingsolution was carried out in four gasification towers arrangedconsecutively (CIOS Report File No. XXI-I5, File XXVll-84, File XXV-44).which are always gassed with a fresh N- -O mixture, which volumewisecorrespond about to the composition of air. The waste gas depleted in Oby passage through the tower is recycled and by dosing with O is broughtto the original composition.

At high contents of tetrahydroanthrahydroquinone derivatives in theworking solution which cause a reduction in the oxidation rate,according to a proposal in Jenney U.S. Pat. No. 3,073,680 attentionshould be paid to the maintenance of specified bubble sizes and crosssection load. Accordingly, the gas distributor should have pore openingsof 0.15 to 0.40 mm. diameter and air is employed in the O N mixturedosed into the towers which are arranged consecutively and have a crosssection load of 36-72 cubic meters/sq. meter X hour (cum/sq. m X 11).

Both described processes have the disadvantage that they are burdenedwith a large apparatus expenditure. It is also a disadvantage that withsmaller pore openings in the gas distributor the gas bubbles becomessmaller whereby the separation of the foam formed causes difficultiesand the means for gas distribution (for example frits) are easilyclogged.

In another process described in Cosby US. Pat. No. 2,902,347 theoxidation is characterized by a countercurrent passage. The hydroquinonesolution to be oxidized is fed to the head of a packed column and flowsagainst the uprising air fed into the bottom of the column. The chargingof this countercurrent is limited by a very low flood level.Furthermore, it has the disadvantage of very great apparatus expensebecause several columns are arranged consecutively if the workingsolution to be oxidized has a high tetra content. In the industrialcarrying out of the cycling of the working solution for months at atime, however, there cannot be avoided the tetracontent of the workingsolution. For these reasons there have been proposed apparatusarrangements for the oxidation of the tetra system which are describedrepeatedly in the literature, for example. Chem. Age. 82. 895 (1958),Chem. and Ind. 1959 page 76, Chem. Process Eng. 40 No. 1. 5 (1959),Brit. Chem. Engng. 4, 88 (1959), and The Ind. Chemist 35, 9 (1959).

In the drawings,

FIG. 1 illustrates the old apparatus arrangement and process employingconcurrent flow,

FIG. 2 illustrates one form of apparatus arrangement and process of theinvention, and

FIG. 3 illustrates a preferred apparatus and process according to theinvention.

Referring more specifically to FIG. 1 both towers l1 and 11a have aheight of 18.3 meters and a diameter of 3.7 meters. The hydroquinoneworking solution is introduced via conduit 50 and conduit 52'to thebottom of tower II and via conduit 50 and conduit 54 to the bottom oftower 11a. Air is similarly introduced via conduit 56 and conduit 58 tothe bottom of tower 11 and via conduit 56 and conduit 60 to the bottomof tower 11a. The air and working solution are forced upward in parallelflow through a layer of packing. The working solution-waste gas mixtureis fed either via conduit 62 to separator 12 or via conduit 64 toseparator 12a where the gas and liquid are separated. The waste gas asshown goes via conduits 66, 68, 70, 72, or 74 to after providedactivated carbon towers 13a or 13b, then via conduits 76 or 78 toactivated carbon towers 130 or 13d. In the activated carbon towers, thewaste gas is freed of residual solvent (working solution) and leaves viaconduits 80 and 82. The residual working solution can then be recoveredand reused. The oxidized working solution leaves the bottom of separator12 via conduit 84 and separator 12a via conduit 86 and is pumped by pump14 to the extraction step.

It has been found that the energy requirements and the apparatus yieldof the oxidation step while retaining the parallel flow from the bottomto the top according to FIG. 1 can be substantially improved if there isemployed, for example. in the oxidation stage, a column provided withobstruction or packing, in which column the hydrogenated workingsolution and the oxidation gas, air or an oxygen containing gas are ledin parallel or concurrent flow from bottom to top in several columns orsections divided in such a way that the section with the highesthydroquinone concentration is provided with the least oxygenconcentration and conversely. If more than two sections are provided asthe hydroquinone concentration goes up from section to section theoxygen concentration goes down.

FIG. 2 shows in schematic fashion one method of carrying out theinvention. The working solution to be oxidized is fed with the help ofpump 88 via conduit 90 to the bottom of packed column 21 and then flowsfrom the top of column 21 via conduit 92 to the bottom of packed column22 and next flows from the top of column 22 via conduit 94 to the bottomof packed column 23. The oxidation gas-fresh gas, e.g., air, is firstintroduced via conduit 96 to the bottom of tower 23 in which thehydroquinone concentration is the lowest and flows in parallel with theworking solution in tower 23 from bottom to top through a packed layer.At the top of each column the gas-liquid mixture is separated bysuitable obstructions such as that at 100. The exhaust gas from tower 23is led via conduit 102 to the bottom of tower 22 and finally via conduit104 to the bottom of tower 21 where the gas which is now greatlydepleted in oxygen is reacted with the fresh working solution whichcontains the highest hydroquinone concentration. The waste gas leavesthe top of tower 21 via conduit 106.

The oxidized working solution is led from the top of tower 23 viaconduit 108 to the buffer feed vessel 24 of the extraction step.

- A preferred form of the invention which is distinquished by anespecially simple apparatus construction in the new oxidation system isshown schematically in FIG. 3. The hydrogenerated working solution flowsinto the bottom of upper section 31 of the packet oxidation tower andthen flows from the top of section 31 to the bottom of section 32 andnext flows from the top of section 32 to the bottom of section 33 of thetower. The oxidation-fresh gas is first fed via conduit 33a into section33 in which the working solution is extensively oxidized and flows inparallel flow from bottom to top, for example, through a packed layer,with the liquid introduced via conduit 33b. In the upper part of thesection, there is provided a device 34a suitable for gasliquidseparation. This upper section is also so designed volumewise that itcan serve as the buffer or feed vessel of the subsequent extractionstep. The liquid can be led off to the extraction step through conduit35. The exhaust gas from section 33 enters section 32 via conduit 32aand subsequently via conduit 31a enters section 31 through which it isagain led from bottom to top in parallel flow with fresh hydroquinonesolution introduced via conduit 31b and the waste gas depleted of oxygenfinally leaves the oxidation tower via conduit 36. The liquid leavingsection 31 at the upper end goes via conduit 32b into section 32 andfrom there, as already mentioned, goes via conduit 33b into section 33.The schematically indicated apparatus for phase separation always shownin the upper part of each section in FIGS. 2 and 3 (FIG. 3 indicated at34a, 34b and 34c) can be situated either outside or inside the trueapparatus or sections. Preferably, it is placed inside whereby it iswell suited as phase separation apparatus of known components, forexample, cyclones working according to the principle of Ter Linden.

The number of individual apparatus which preferably are composed assections of an oxidation tower depends upon various degrees ofinfluence, for example, of speed of oxidation and tetra content of theworking solution, reaction temperature, pressure, oxygen content of thegas feed. Since air is the preferred oxidation gas for carrying out theprocess of the invention, the number of apparatus (i.e., sections)ranges between 2 and 6, especially between 2 and 4. Of course, by usinga larger number of sections the advantages specified below areincreased. However, in such a case there is also an increased apparatusexpense.

In the apparatus (sections) in which the liquid-gas mixture always isled in parallel flow from bottom to top in order to provide thoroughinner mixing there can be provided suitable obstructions. Theseobstructions, for example, can be bubble caps or grids. Packing can alsobe employed in their place. Preferably there is used packing havingdimensions of abaout 15 to mm., especially of 25 to 50 mm. The height ofthe layers in which an exchange of materials in the phases occurs isdesignated as the effective height. Collectively the effective height ofall sections in a given case composited to a column, should amount to 8to 25 meters, especially 10 to 18 meters. Surprisingly, it was foundthat the process of the invention, despite the smaller effective heightof the apparatus, can be carried out so that in a composite column, thesections can employ very high liquid cross sectional loads namely 10 to55 cum/sq. m X 11, especially 15 to 35 cu.m/sq. m X I1. This results inan especially good apparatus yield, which is connected to furtheradvantages. The stated load limits again depend upon many factors(composition, tetra content, viscosity, surface tension and ca pacity ofthe work solution, size of the packaging, oxidation temperature,pressure, etc.), especially, however, they depend upon the amount ofoxygen containing gas necessary for the oxidation. lf air is employed asthe oxidizing gas in the invention process then the gas cross sectionalload (based on the free, unfilled column cross section) of 370 to 2,050normal cubic meters/sq. meter X hour, especially 550 to 1,300 N cu.m/sq.m X h. The cross sectional loads are at least twice as high as in thepreviously known processes.

The process of the invention can be carried out at normal pressure orincreased pressures of 1 to 7 atmosphere absolute. The temperature canalso be varied within wide limits, for example from 20 to C. Since ahigh temperature increases the rate of oxidation and permits high crosssectional loads on the one hand but on the other hand, cause increasedbreakdown of product formation, temperatures in the range of 45 to 75 C.are preferred.

The process of the invention can be employed for the oxidation of allknown working solutions used in the anthraquinone process. The processis especially suitable for working solutions which employ as reactioncarriers alkyl anthraquinone, 2-methyl anthraquinone, 2-butylanthraquinone, 2-isopropyl anthraquinone, 2- sec., amyl anthraquinone,l, 3 dimethyl anthraquinone, 2, 7-dimethyl anthraquinone and mixtures ofthese as well as their partially nuclear hydrogenated derivatives, e.g.,the tetrahydro anthraquinones such as 2-ethyl tetrahydro anthraquinone.As quinone solvents there can be used for example aromatic hydrocarbonssuch as tctramethyl benzene, t-butylbenzene, diphenyl, naphthalene,diethyl benzene, utetrahydronaphthalene, xylene, methyl naphthalene,mixtures of aromatic hydrocarbons boiling at l85205C., as hydroquinonesolvents there can be used for example. phosphates or phosphonat'es suchas trioctyl phosphate, tributyl phosphate, triamyl phosphate, dioctylphenyl phosphonate. trihexyl phosphate and tridecyl phosphate. alcoholssuch as octanol-2, esters such as methyl cyclohexyl acetate. Workingsolutions of this type contain stable components and therefore permithigh cross sectional loads, high oxidation rates and high temperatureswhereby especially favorable apparatus yields results.

The most substantial advantages of the process of invention incomparison to the known ways of carrying out the oxidation steps aresummarized below:

1. Lower apparatus expense, i.e,, lower investment cost.

2. Lower energy requirements. i.e., lower operation costs.

3. Lowerliquid holdup in the apparatus; which corresponds to a shortresidence time of the working solution in the apparatus, which issynonymous with a lowering of decomposition product formation.

4. The system makes possible the oxidation of working solutions withhigh tetra contents,

5. High cross sectional loads for gas and liquid which are at leasttwice as high as in known processes; accompanying this there areindustrially favorable apparatus yields at degrss of oxidation which areover 97 percent frequently even over 99 percent.

6. Cessation of operation disturbances by clogging of the gasificationcandle and/or strong form development.

7. Cessation of intermediate closing of gas and liquid.

ln the following comparison examples two typical working experiments aredescribed which are carried out according to the known process (FIG. 1,Example 1) and according to the process of the invention (FIG. 3,Example 2). By the illustrative examples the advantages of the processof the invention are made evident. The process of the invention,however, is not limited to the illustrative form selected.

Unless otherwise indicated all parts and percentages are by weight.

EXAMPLE 1 a as the reaction carrier 90 grams of 2-ethyltetrahydroanthraquinone plus grams of ethyl anthraquinone per liter. Thesolvent consisted of a mixture of 75 volume percent of aromatichydrocarbons (boiling range l85-205C) and 25 volume percent tri (2-ethylhexyl) phosphate. The flow of the working solution through thecyclic apparatus amounted to 130 cu. meters/hour, In the hydrogenationstep the working solution was hydrogenated to the extent that there wasformed a working solution having an amount of hydroquinone correspondingto an H 0 equivalent of about 9.45 kg/cu.m. The working solution was ledthrough an oxidation tower (analogous to lower 11 in FIG. 1) which wasfilled with 25 X 25 mm. ceramic Raschig rings, and had an effective ofheight of 20 meters and a diameter of 3.7 meters. Together with theworking solution there was fed into the bottom of the column 5,000normal cubic meters of air/hour (pressure at the bottom of the column3.0 atmospheres absolute; pressure at the top of the column 1.5atmospheres absolute), in which a mean temperature of 54C. prevailed. Inthis manner of operation there was produced a 98.1% overall oxidation inwhich the 0 content of the waste gas amounted to 6 percent and a currentrequirement of 0.44 kilowatt/kg H 0 was measured as the share for theair compresser.

EXAMPLE 2 260cu.m/h of a working solution having the same compositionand hydroquinone content as in example 1 was fed through an oxidationtower according to FIG. 3 together with l0,000 normal cu. m. of air/h,This tower also had a diameter of 3.7 meters and was divided into threesections which together had an effective height of only 15 meters. Atthe same pressure and temperature conditions as in Example 1, there wasobtained an overall oxidation of 98.3% and the 0 content of the wastegas was below 5.9% and there was a current requirement of 0.36kilowatt/kg. H 0 measured as the share for the air compressor.

What we claim is:

1. In an apparatus for forming hydrogen peroxide by the cyclicanthraquinone process employing a working solution comprising a columnfor hydrogenating the working solution and a separate column foroxidizing the working solution and wherein liquid flows from the bottomto the top of said separate column. the improvement comprising columnmeans for oxidizing the working solution made of a plurality ofvertically disposed, vertically aligned column sections including afirst lower section and a second upper section, conduit means forintroducing an oxygen containing gas to the bottom portion of said firstsection, conduit means for conducting working solution lowest inhydroquinone concentration and separated from the top portion of saidsecond section into the bottom portion of said first section, cyclonemeans in the top portion of said first section for separating gas andworking solution, conduit means connected to the top of said firstsection for removing the separated working solution, extractor means forremoving hydrogen peroxide from the working solution, conduit means forreturning the working solution to the hydrogenation means of the cyclicprocess, conduit means for leading the gas separated from the top ofsaid first section to the bottom of said second section, conduit meansfor introducing working solution to the bottom of the second section,cyclone means in the top portion of said second section for separatinggas and working solution and conduit means for removing gas from the topportion of said second section.

2. An apparatus according to claim 1 wherein there are 2 to 6 of saidsections in the oxidizing column, each section above the bottom sectioncontaining conduit means in the bottom portion for introducing gas fromthe top portion of the next lower section and each sec-.

tion below the top section containing separate conduit means in thebottom portion for introducing working solution from the top portion ofthe next higher section, conduit means for introducing gas into thebottom portion of the lowermost section, conduit means for introducingworking solution into the bottom portion of the topmost section andcyclone means for separating gas from working solution in the topportion of each section, conduit means for passing working solution outof 6. An apparatus according to claim 1, wherein there is providedobstruction means in the bottom of the sections in the oxidizing columnand both the conduit means for introducing the working solution at thebottom of each section and the conduit means for introducing gas at thebottom of each section have their inlet to each section below saidobstruction means to provide thorough mixing of the working solution andgas.

1. IN AN APPARATUS FOR FORMING HYDROGEN PEROXIDE BY THE CYCLIC ANTHRAQUINONE PROCESS EMPLOYING A WORKING SOLUTION COMPRISING A COLUMN FOR HYDROGENATING THE WORKING SOLUTION AND A SEPARATE COLUMN FOR OXIDIZING THE WORKING SOLUTION AND WHEREIN LIQUID FLOWS FROM THE BOTTOM TO THE TOP FO SAID SEPARATE COLUMN, THE IMPROVEMENT COMPRISING COLUMN MEANS FOR OXIDIZING THE WORKING SOLUTION MADE OF A PLURALITY OF VERTICALLY DISPOSED, VERTICALLY ALIGNED COLUMN SECTIONS INCLUDING A FIRST LOWER SECTION AND A SECOND UPPER SECTION, CONDUIT MEANS FOR INTRODUCING AN OXYGEN CONTAINING GAS TO THE BOTTOM PORTION OF SAID FIRST SECTION, CONDUIT MEANS FOR CONDUCTING WORKING SOLUTION LOWEST IN HYDROQUINONE CONCENTRATION AND SEPARATED FROM THE TOP PORTION OF SAID SECOND SECTION INTO THE BOTTOM PORTION OF SAID FIRST SECTION, CYCLONE MEANS IN THE TOP PORTION OF SAID FIRST SECTION FOR SEPARATING GAS AND WORKING SOLUTION, CONDUIT MEANS CONNECTED TO THE TOP OF SAID FIRST SECTION OF REMOVING THE SEPARATED WORKING SOLUTION, EXTRACTOR MEANS FOR REMOVING HYDROGEN PEROXIDE FROM THE WORKING SOLUTION, CONDUIT MEANS FOR RETURNING THE WORKING SOLUTION TO THE HYDROGENATION MEANS OF THE CYCLIC PROCESS, CONDUIT MEANS FOR LEADING THE GAS SEPARATED FROM THE TOP OF SAID FIRST SECTION TO THE BOTTOM OF SAID SECOND SECTION, CONDUIT MEANS FOR INTRODUCING WORKING SOLUTION TO THE BOTTOM OF THE SECOND SECTION, CYCLONE MEANS IN THE TOP PORTION OF SAID SECOND SECTION FOR SEPARATING GAS AND WORKING SOLUTION AND CONDUIT MEANS FOR REMOVING GAS FROM THE TOP PORTION OF SAID SECOND SECTION.
 2. An apparatus according to claim 1 wherein there are 2 to 6 of said sections in the oxidizing column, each section above the bottom section containing conduit means in the bottom portion for introducing gas from the top portion of the next lower section and each section below the top section containing separate conduit means in the bottom portion for introducing working solution from the top portion of the next higher section, conduit means for introducing gas into the bottom portion of the lowermost section, conduit means for introducing working solution into the bottom portion of the topmost section and cyclone means for separating gas from working solution in the top portion of each section, conduit means for passing working solution out of the top portion of the lowermost section and conduit means for passing gas out of the top portion of the top section.
 3. An apparatus according to claim 2 having three sections.
 4. An apparatus according to claiam 1 wherein each column is packed and each bottom portion includes means for thoroughly mixing the gas and working solution.
 5. An apparatus according to claim 1 wherein the combined sections have a height of 8 to 25 meters.
 6. An apparatus according to claim 1, wherein there is provided obstruction means in the bottom of the sections in the oxidizing column and both the conduit means for introducing the working solution at the bottom of each section and the conduit means for introducing gas at the bottom of each section have their inlet to each section below said obstruction means to provide thorough mixing of the working solution and gas. 